(a) Field of the Invention
This invention relates to valve activating systems for use in fluid handling systems, which valve activating systems are responsive to changes in thermal conditions. More specifically it relates to freeze condition responsive safety systems in the form of thermostatically controlled valves which automatically purge water from water supply lines at the approach of freezing temperatures, and which terminate the purging action when the danger of freezing has passed.
(b) Discussion of the Prior Art
It is well known that when water freezes, it expands. This expansion can result in cracking and other damage to closed systems such as containers and pipes. When a water pipe freezes and cracks it causes, at a minimum, the inconvenience and expense of replacement, and if in a building structure can cause flooding and other related structural damage. It is not unusual for those seeking to avoid freeze damage to go to the time, trouble and expense of draining exposed water lines, or wrapping them with electrical resistive heating tape, or maintaining them in a constant "on" position so that the flow of water will prevent the build-up of ice in the pipes. Unfortunately, these methods can be inconvenient, expensive and unreliable.
A number of thermally activated devices for opening and closing valves and drains in response to changes in temperature are known in the art. In most instances, these devices have been directed at the prevention of damage to water systems as a result of freezing. For example, U.S. Pat. No. 503,932 discloses devices which can be connected to a water line, and which includes a linear bimetallic device which terminates in a valve closing element. The valve closing element of this patent is caused to open said valve and allow the drainage of fluid from a connected pipe in response to temperatures approaching the freezing point. In the system of this reference, the bimetallic thermostatic elements are located in such a manner that they are engulfed by fluid, both before and during their operation. U.S. Pat. No. 1,200,928 discloses a valve controlling mechanism for water pipes, which while isolated from contact with the fluid, is quite complex in its structure and operation. U.S. Pat. No. 1,508,872 discloses yet another freeze preventing thermostatic control device which utilizes a bimetallic system to actuate a valve to release fluid in response to low temperatures. However, the device of this reference is mechanically complex and allows the fluid to drain through the thermostatic mechanism.
Of perhaps greatest interest to the present invention is U.S. Pat. No. 2,214,844 which discloses an automatic drain device which utilizes a simple bimetallic coil mechanism having an extension thereof in contact with a valve activating device for the opening and closing of the valve in response to the approach of freezing temperatures. However, the thermostatic coil is located in a housing which is constantly immersed in liquid.
Other prior art which discloses temperature responsive drain valves includes U.S. Pat. No. 330,664 and U.S. Pat. No. 4,456,024.
It is thus seen that it would be desirable to have a simple, inexpensive system for draining water lines at the approach of freezing temperatures, and in which the activating mechanism is maintained out of contact with the fluid both during and after its activation.